He appeared to be going for the force choke in ANH after the officer reports that there is no Rebel Base on Tatooine. Vader tells Tarkin that "she would never consciously betray the Rebellion" then his hand looks like it is doing the force choke. What's up with that?

Poor audio editing. That's always irritated me a bit. Vader's said his bit, but continues to elucidate briefly with his hands (presumably the on-set audio would have been Prowse continuing his dialogue).

It's just a mistake, nothing more. Given the ridiculously tight schedule they were all on, it's surprising that there aren't more of these sort of errors (the 'ghost' in the Falcon cockpit, the stormtrooper banging his head, couple of lightsaber FX missed) than there are in the original film.

This thing with Vader's hands is about the only one I find even mildly irritating in any way, largely because it's Vader, who otherwise dominates every second of the nine minutes or so he's on screen like no other character since Harry Lime in 'The Third Man'.

I always wondered why the names were so similar. Two planets orbiting one sun, okay. Two planets colonized by the same religious cult, okay. But as far as I know the planets were not connected in any way, except for nearly identical names. Did that ever strike you as strange?

Dave Prowse was intentionally exaggerating his gestures to better aid voice looping that would occur during post-production. You couldn't see his mouth so he frequently moves gratuitously at the director's instruction to help cue his dialogue added later. Personally, I think his pronounciated movements only made the character appear even more menacing.

(Hey, Callista, it's my first visit to the board too in almost five years! And yes, it is strange that Lucas chose the name Dantooine since it would reasonably confuse a casual viewer)

Dave Prowse was intentionally exaggerating his gestures to better aid voice looping that would occur during post-production. You couldn't see his mouth so he frequently moves gratuitously at the director's instruction to help cue his dialogue added later. Personally, I think his pronounciated movements only made the character appear even more menacing.

In this case, though, it's an actual mistake. His hand gestures are over dead silence, & they're the sort of gestures clearly meant to accompany dialogue. They don't lead into any further dialogue from Vader, either.

I was under the impression there was some additional dialogue that was cut out. Something along the lines of "I told you she would never consciencely betray the rebellion, unless it meant destroying us as well."

I think it's funny that C3PO even wonders which planet he's on and Luke doesn't even tell him the name, then later an Imperial officer tells Tarken the Falcon matches the description of a ship that "Blasted it's way out of Mos Eisley"

Poor audio editing. That's always irritated me a bit. Vader's said his bit, but continues to elucidate briefly with his hands (presumably the on-set audio would have been Prowse continuing his dialogue).

It's just a mistake, nothing more. Given the ridiculously tight schedule they were all on, it's surprising that there aren't more of these sort of errors (the 'ghost' in the Falcon cockpit, the stormtrooper banging his head, couple of lightsaber FX missed) than there are in the original film.

This thing with Vader's hands is about the only one I find even mildly irritating in any way, largely because it's Vader, who otherwise dominates every second of the nine minutes or so he's on screen like no other character since Harry Lime in 'The Third Man'.

harry lime in The Third Man?

A Film Noir fan, eh?

And you'd pick Harry Lime over, say,....

Cody Jarrett in White Heat:

"Made it Ma, Top of the world!."

Not to mention...

Captain Queeg in The Cain Mutiny:

"Ah, but the strawberries, that's when I had them..."

Or Dinero in Raging Bull?

Or, Ray Miland in The Lost Weekend?

Or, Jeff Bailey: "Oh, I may die, but I'll be the last one." in 'Out of the Past'?

That's not actually the first public source for The Duel, that's from Star Wars Poster Monthly #2, November 1977. George Lucas revealed it a bit earlier to Rolling Stone in August of 1977:

Why does Darth Vader breathe so heavily?
I had wanted to do that and tie it in with the dialogue.It was a nice touch, because it adds to the bogyman quality of the character.
Ben had a lot of work in that too. He did about 18 different kinds of breathing, through aqualungs and through tubes, trying to find the one that had the right sort of mechanical sound, and then decide whether it would be totally rhythmical and like an iron lung. That's the idea. It was a whole part of the plot that essentially got cut out. It may be in one of the sequels.What's the story?
It's about Ben and Luke's father and Vader when they are young Jedi knights. But Vader kills Luke's father, then Ben and Vader have a confrontation, just like they have in Star Wars, and Ben almost kills Vader. As a matter of fact, he falls into a volcanic pit and gets fried and is one destroyed being. That's why he has to wear the suit with a mask, because it's a breathing mask. It's like a walking iron lung. His face is all horrible inside. I was going to shoot a close-up of Vader where you could see the inside of his face, but then we said, no, no, it would destroy the mystique of the whole thing.

SW Poster Monthly was obviously taking their information from the RS interview. The bit about "suffering Tarkin as a pawn in a larger game plan" seems to be their take on a passage in the novelisation:

Vader stared at the motley array of stars
displayed on the conference-room map while
Tarkin and Admiral Motti conferred nearby.
Interestingly, the first use of the most
powerful destructive machine ever constructed
had seemingly had no influence at all on that
map, which in itself represented only a tiny
fraction of this section of one modest-sized
galaxy.
It would take a microbreakdown of a portion
of this map to reveal a slight reduction in
spatial mass, caused by the disappearance of
Alderaan. Alderaan, with its many cities,
farms, factories, and towns - and traitors,
Vader reminded himself.
Despite his advances and intricate
technological methods of annihilation, the
actions of mankind remained unnoticeable to an
uncaring, unimaginably vast universe. IfVader's grandest plans ever came to pass, allthat would change.
He was well aware that despite all their
intelligence and drive, the vastness and
wonder were lost on the two men who continued
to chatter monkeylike behind him. Tarkin andMotti were talented and ambitious, but theysaw things only on the scale of humanpettiness. It was a pity, Vader thought, thatthey did not possess the scope to match theirabilities.Still, neither man was a Dark Lord. As such,little more could be expected of them. Thesetwo were useful now. and dangerous, butsomeday they, like Alderaan, would have to beswept aside. For now he could not afford toignore them. And while he would have preferred
the company of equals, he had to admit
reluctantly that at this point, he had no
equals.

Tarkin can stop Vader from choking someone. He is extremely powerful, and Palpatine holds him in a similar place of value. Vader would not get away with killing Tarkin (during ANH, at least). He would not even have the guts.